The present invention relates generally to the field of heat sinks and more specifically to the field of heat sinks configured to self-align with heat generating devices that may not be parallel to the heat sink.
Modern electronics have benefited from the ability to fabricate devices on a smaller and smaller scale. As the ability to shrink devices has improved, so has their performance. Unfortunately, this improvement in performance is accompanied by an increase in power as well as power density in devices. In order to maintain the reliability of these devices, the industry must find new methods to remove this heat efficiently.
By definition, heat sinking means that one attaches a cooling device to a heat-generating component and thereby removes the heat to some cooling medium, such as air or water. Unfortunately, one of the major problems in joining two devices to transfer heat through a common surface is that a thermal interface is created at the junction. This thermal interface is characterized by a thermal contact impedance. Thermal contact impedance is a function of contact pressure, surface finish, and gap size. Thermal contact impedance also raises dramatically when the surfaces of the two devices are non-parallel. With non-parallel devices, only a small percentage of the possible contact area between the two devices is actually in contact and conducting heat.
As the power density of electronic devices increases, heat transfer from the heat generating devices to the surrounding environment becomes more and more critical to the proper operation of the devices. Many current electronic devices incorporate heat sink fins to dissipate heat to the surrounding air moving over the fins. These heat sinks are thermally connected to the electronic devices by a variety of techniques. Some devices use a thermally conductive paste in an attempt to lower the contact resistance. Others may use solder between the two elements both for mechanical strength and thermal conductance. Once again, if the two surfaces to be thermally coupled are not parallel difficulties may arise since the region of contact between the two surfaces forms a line instead of a plane. Thermal paste and solder are only usable for junctions with small amounts of non-co-planarity.
Many present electronic modules include a plurality of heat-generating electronic devices on a single substrate. Often these devices do not have a co-planer upper surface that would allow a single heat sink to be thermally coupled to the plurality of devices. Thermal paste and other thermally conductive materials, such as solder, may be used to fill small gaps between the heat-generating electronic devices and the single heat sink, however large gaps are often not capable of being filled by a paste or solder. In such cases, multiple heat sinks may be used, however, this adds cost and reduces the efficiency of the heat dissipation.
A heat-activated self-aligning heat sink is built thermally connecting at least one heat-generating devices on a substrate to the heat sink body, where the heat-generating devices may not be co-planar with each other due to tolerance stack-up or parallel with the heat sink body. A pedestal is attached to the substrate to support the heat sink body. A plug or floating pedestal is placed on top of each heat-generating device and held within the pedestal allowing sufficient movement for the bottom surface of the plug to fully contact the top surface of the heat-generating device. A quantity of a low melting temperature, thermally conductive material, such as solder, or a thermally conductive liquid, is placed over each plug and a heat sink body is placed over the assembly. When heated, the thermal material melts, forming a low impedance thermal junction between the plug and the heat sink body regardless of planarity differences between the two devices.